The relationships of acid-base parameters in arterial blood and CSF to regulation of respiration are under study in animals in the state of natural hibernation. Two species of marmots and one species of ground squirrel (C. lateralis) are used. Baseline parameters of body temperature, heart rate, and respiratory rate are measured during entry to hibernation, basal hibernation, and spontaneous arousal from hibernation. The effects of alteration in ambient PCO2, and of infusion of CSF of altered (HCO3) are to be investigated in detail.